$Pb(Mg_{1/3} Nb_{2/3})O_3$ - $PbTiO_3$ (PMN-PT) is widely used as electronic components because of its excellent dielectric, piezoelectric and electrostrictive properties. To use PMN-PT ceramics on a material for electro-active systems, high reliability in mechanical properties is also needed. The chemically induced interface migration (CIIM) may be a technique to modify the microstructure and mechanical properties. In the present study, we investigated the CIIM in 0.65PMN-0.35PT and its effect on mechanical properties.
PMN-PT samples were produced using the Columbite precursor method. When $CaTiO_3$, $BaTiO_3$, PMN or PT particles were scattered on polished surfaces of sintered PMN-PT and then annealed, the PMN-PT grain boudaries migrated. Near the scattered particles, grain boundaries were corrugated and thus the grain shape changed from a normal one to irregular ones. Especially, near the scattered PT particles, fast grain growth occured. This result indicates that the interface migration was induced by alloying of external solute atoms in PMN-PT grains, as in usual CIIM. PT was the most compatible solute source to induce the CIIM in PMN-PT. The coherency strain energy was calculated in case of the addition of PMN or PT to PMN-PT. The calculation showed that higher coherency strain energy was induced in case of PMN adding because of higher alloying of Mg and Nb than of Ti. Surface modified PMN-PT samples were prepared sintering PMN or PT powder-packed PMN-PT. Evaluation of the mechanical properties by Hertzian indentation and Vickers indentation showed that $P_Y$ value and hardness of the PT-packed sample were higher than those of the unpacked sample. The mechanical properties were thus improved in the samples with a CIIM layer. The CIIM was also observed when the PMN-PT samples containing PT powder agglomerates were sintered. This result suggests that CIIM can be induced inside the samples as well as in the surface region.
